Piston-primer cartridge



Nov. 11, 1969 I. R. BARR 3,477,375

PISTON-PRIMER CARTRIDGE Filed April 11. 1968 2 sheets sheeft"l Ir win R.Barr INVENTOR glam/7w ATTORNEY Nov. 11, 1969 l. R. BARR 3,477,375

uswowmmm CARTRIDGE 7 Filed April 11, 1968 2 Sheets-Sheet 2 ATTORNEYUnited States Patent ()lfice 3,477,375 Patented Nov. 11, 1969 3,477,375PISTON-PRIMER CARTRIDGE Irwin R. Barr, Lutherville, Md., assignor to AAICorporation, Cockeysville, Md., a corporation of Maryland Filed Apr. 11,1968, Ser. No. 720,549' Int. Cl. F42b 5/28 US. Cl. 102-45 ABSTRACT OFTHE DISCLOSURE A cartridge is disclosed having a single-unit movablepiston primer for use in automatic and semi-automatic fire-arms whichoperate on the principle of primer setback. The single-unit pistonprimer is cup-shaped with a 7 Claims circumferential rim-fire rear walland contains a primer charge. The cup-shaped piston primer is opentoward the This invention relates to cartridges of the primer setback orpiston-primer type.

In automatic or semi-automatic firearms utilizing primer set-backcartridges for operation, a cartridge may be chambered in the barrel,and when the firing pin of the firearm strikes the primer in a forwardstroke, a primer charge ignites which, in turn, ignites a propellant tocreate a high gas pressure that propels a projectile forward from thecartridge casing and through the barrel. The high gas pressure alsopropels the primer rear- Wardly in the direction opposite to the motionof the projectile. The rearward movement of the primer imparts energy tothe firing pin and drives it rearwardly in a return stroke whichoperates the breech mechanism to extract the spent cartridge casing,cock the firearm and chamber another cartridge.

To obtain the most effective operation of a primer setback arrangement,it is necessary to use a cartridge which maximizes the amount of energythe piston primer imparts to the firing pin of the firearm during thereturn stroke. This can best be done by minimizing the amount of energydissipated by the friction between the piston primer and the cartridgeduring its rearward movement while at the same time preventing thepropellant gas from leaking rearward of the piston primer in a mannerwhich would substantially reduce the differential gas pressure exertedon the piston primer and hence reduce the force driving the pistonprimer rearward. Furthermore, it is desirable to prevent the pistonprimer from being blown out the base of the cartridge because theresulting sharp reduction of the propellant gas pressure wouldsubstantially reduce the velocity of the projectile and hence afiect therange and accuracy of the weapon. In addition, it is desirable that thepiston primer be constructed of as few parts as possible to facilitatethe manufacture of the cartridge and reduce the production costs.

Accordingly, it is a feature of the present invention to provide acartridge of the primer set-back type wherein frictional retardingforces on the piston primer during its rearward movement are minimizedwhile efliciently translating propellant gas pressure action intorearward driving force on the piston primer; thereby enabling a maximumdriving force to be imparted to the firing pin of the firearm during thereturn stroke, while also providing a gas seal to prevent the rearwardleakage of the high pressure propellant gas to further maximize theamount of force exerted on the piston primer.

It is another feature of the present invention to provide a pistonprimer in which an obturating gas seal on the piston primer is adaptedto engage the cartridge casing at the end of the rearward drivingmovement to prevent the piston primer from being blown out the base ofthe cartridge by the propellant gas forces.

It is a further feature of the present invention to provide a pistonprimer having a simple, compact, and unitary construction to facilitatethe manufacture of the cartridge and reduce the production costs.

In accordance with the present invention, a cartridge is provided havinga casing with a pair of interconnected longitudinally arranged coaxialbores, the large-r diameter bore containing a propellant and the smallerdiameter bore having a movable cup-shaped piston primer disposed thereinwhich opens toward the interior of the casing and contains a primermixture adapted to be ignited and fire the propellant in the largerdiameter bore. The movable cup-shaped piston primer has a relativelythick-walled deformation-resistant tubular wall portion freely slidablyengaging the smaller diameter bore with a relatively thinner and moreeasily deformable base portion extending rearward thereof which isprebent or preshaped to form a circumferential rim anvil or arranged tobe easily bent upon being struck by the head of a firing pin to form acircumferential rim anvil which in turn is adapted to ignite the primercharge. At the open end of the tubular wall portion is formed an annularflared obturating flange portion with only a small circumferentialsurface area slidably engaging the larger diameter bore in a lightinterference fit for gas sealing action and maximizing of energytransfer to the piston primer. The forward longitudinal movement of thepiston primer is limited by a stop formedi n the larger diameter borefor engagement by the forward edge of the flared flange portion of thepiston primer, while the rearward longitudinal movement of the pistonprimer is limited by the engagement of the back side of the flaredobturating flange portion with an annular beveled shoulder connectingthe coaxial bores.

When the head of a firing pin strikes the base of the cup-shaped pistonprimer at the end of a forward stroke, the circumferential rim anvil iscrushed to ignite the primer charge which in turn fires the propellantto create a high gas pressure that propels a projectile from thecartridge while at the same time acting across the full cross-sectionalarea of the open end of the piston primer which occupies the fullcross-sectional area of the larger diameter propellant-containing boreto impart a maximum rearward force to the piston primer to drive itrearwardly. Because the interference fit obturating flange portion hasonly a small surface area engaging the larger diameter bore, and thethick-walled tubular rear portion of the primer freely slidably engagesthe smaller diameter bore, the retarding frictional forces incurredduring the rearward movement of the piston primer are minimized toenable it to drive the firing pin backward in a return stroke andtransfer a maximum amount of energy to operate the breech mechanism,extract the spent cartridge, cock the firearm and chamber anothercartridge.

Still other objects, features, and attendant advantages will becomeapparent to those skilled in the art from a reading of the followingdetailed description of several physical embodiments constructed inaccordance with the present invention, taken in conjunction with theaccompanying drawings wherein:

FIG. 1 shows a longitudinal cut-away view of a cartridge according tothe invention.

FIG. 2 shows the cartridge of FIG. I inserted in the chamber of afirearm with a bolt engaging the base of the cartridge and having afiring pin in the ready position.

FIG. 3 is a view similar to FIG. 2, showing the firing pin shortly afterstriking the base of the primer and igniting the propellant to providethe projectile-propelling high gas pressure.

FIG. 4 is a view similar to FIGS. 2 and 3, showing the movable primerpropelled rearward by the propellant gas pressure which forces thefiring pin backward in a return stroke.

FIG. 5 illustrates a second embodiment according to the invention,incorporating a two-piece single-unit piston primer having a thin,easily deformable, outer cup portion surrounding a relativelythick-walled inner reinforcing member which is open at both ends andserves as a circumferential anvil, cylindrical guide sectionreinforcement, and obturating element.

FIG. 6 illustrates a third embodiment according to the invention,incorporating a single-unit cup-shaped piston primer composed of asingle piece, the rear section of which is preformed as a self-formingcircumferential rim hammer and anvil.

Referring now in detail to the figures of the drawings, in FIG. 1 isshown a cartridge suitable for use in a gun which is operated on theprimer set-back and energy transfer principle. The cartridge, generallyindicated at 11, includes a casing, generally indicated at 13,containing a movable single-unit piston primer, generally indicated at15, a projectile 21 and propellant 31 disposed between the movablepiston primer 15 and the projectile 21. The cartridge casing 13 has twocoaxial bores of different diameters, indicated respectively at 13b and13d, and connected through an annular beveled shoulder 130, with thesmaller guide bore 13d being located at the rear of the cartridge casing13 and the larger gas-retaining bore 13b being located at the forwardend of the casing 13 and adapted to securely grip an annular groove 21aof the projectile 21 by means of an annular indentation 13c. Thesingle-unit, cup-shaped, piston primer 15 has a cylindrical pistonguiding portion 15a opening forwardly toward the interior of the largerdiameter propellant chamber bore 13b with an annular, flared,obturating, flange portion 15d formed at the open mouthed forward endthereof. The cylindrical guide portion 15a has an integrally connected,thin-walled rear or base cup portion 15b which is of smaller diameterthan the cylindrical guide portion 15a. An external annular shoulder 150is formed at the junction of the base cup portion 15b and thecylindrical guide portion 15a, this shoulder serving as an effectivecircumferential anvil when the base cup portion is crushed against itupon being struck by the firing pin and further serves, in conjunctionwith the firing pin, to provide a tight fitting internal chamber seal toprevent the relatively thin-walled base cup from being laterallyruptured by the high gas pressure resulting from ignition of thepropellant.

The cylindrical piston guiding portion 15a of the primer 15 is freelyslidably disposed in the small diameter bore 13d at the rear of thecartridge casing 13 while the edge of the flared flange portion 15dslidably engages the larger diameter bore 13b in a light interferencefit. In its unfired position, the edge of the flared flanged portion 15dengages an annular forward shoulder stop as shown at 13a, oralternatively, circumferentially spaced dimple stops, which limits theforward motion of the primer piston. Compacted in the cup-shapedcylindrical portion 15a is the primer charge 17, which may be ofconventional composition, and which is separated from the propellant 31near the open-mouthed end of the cup-shaped piston by only a thin easilyfrangible and preferably combustible moisture seal 19 of suitablematerial such as a coating of wax or Krylon. While the moisture seal 19is not absolutely required for functional operation, it is desirable toaid against malfunction due to undesired moisture absorption by theprimer mix which, for example, might occur during assembly.

In FIGS. 24 is illustrated the operation of the cartridge shown inFIG. 1. In FIG. 2, a cartridge is shown inserted in a chamber 41a of aconventional barrel 41 having a bore 43 with a bolt 51 pressed againstthe base of the cartridge casing 13 and having the finger 52a of anextractor 52 engaging an extractor groove 13 formed in the rear of thecartridge casing 13. Disposed inside the bolt 51 is a firing pin 61having a head 61a for striking the deformable, cup-shaped base 15!) ofthe cup-shaped piston primer 15 so as to cause ignition of the primercharge 17 and the propellant charge 31.

In FIG. 3 is shown the head 61a of the firing pin 61 striking the base15b of the piston primer 15 at the end of a forward stroke. The base 15bof the piston primer 15a is crushed and pressed against the end of theexternal annular shoulder 15c at the end of the relatively thickwalledcylindrical portion, which effectively forms a circumferential rimanvil, thereby igniting the primer charge. In addition, the head 61a ofthe firing pin 61 and the external annular shoulder 15c coact to providea seal which prevents any lateral rupture of the thin-walled base 15b ofthe cup-shaped primer. The ignition of the primer charge 17 ignites thepropellant charge 31, which generates a high gas pressure that propelsthe projectile 21 and at the same time obturates the flared annularflange 15d of the primer 15 against the large diameter bore 13b of thecartridge casing 130 and thereby prevents gas leakage to the rear of theflange portion 15d. With the relatively thick-walled construction of thecylindrical piston portion 15c, the cylindrical guide portionsubstantially resists expansion from the high gas pressure upon ignitionof the propellant 31, and remains easily slidable within the smalldiameter bore to deliver a maximum amount of force to the firing pin 61to drive it backward in a return stroke.

The single-unit piston primer is propelled backwards by the high gaspressure to the rear of the cartridge casing 13 until the back side ofthe flanged portion 15d engages the annular, beveled shoulder 130 whichstops the rearward longitudinal movement of the piston primer 15, asshown in FIG. 4. In addition, the high gas pressure forces thethin-walled base 15b of the cup-shaped piston to bulge rearwardly in asemispherical shape. The rearward motion of the cup-shaped piston primer15 forces the firing pin 61 backward in a rearward return stroke toopeate the breech mechanism and/ or other components of the firearm.

In FIG. 5 is shown another embodiment of a cartridge suitable for use ina firearm employing the primer setback and energy transfer principle. Inthis embodiment, generally indicated at 111, the movable primer iscomposed of two unitarily connected pieces 115a and 115b. The firstpiece 115a is cup-shaped and relatively thin-walled and forms theannular exterior of the primer 115, which has a rear surface portion115s which is formed by the thinner walled piece 115a and which slidablyengages a small diameter bore 113d at the base of the cartridge casing113 in a loose sliding fit. An annular outwardly flared flanged portion115a is formed at the open end of the cup-shaped piece 115a, the annularlip of which slidably engages the large diameter bore of the cartridgecasing in a light interference fit. Secured tightly within thethin-walled piece 115a is an annular member 115b having a bore coaxialwith the cup-shaped portion of the thin-walled piece 115a and an outerannular surface which is contiguous with the interior surface of thethin-walled piece 115a. The inner member 11512 has a relativelythickwalled, cylindrical section 115])" for annular reinforcement ofthinner-walled section 115a" forming the rear surface portion 1150. Alsoformed at the forward open end of the inner cylindrical member 1151') isan outwardly flared flange 1151;, the outer lip of which issubstantially thinner than cylindrical wall section 115b", and which inconjunction with the contiguous lip of the annular flange 115a, servesas a pressure responsive obturator seal.

Although the thick-walled member 115b is contained within thethin-walled member 115a the longitudinal extent of the thick-walledmember is less than that of the thin-walled member 115a to form arim-like cavity between the base of the thin-walled member 115a and therear end surface of the thick-walled member 115b. The primer charge 117is contained in the bore of the thickwalled member 115b and in thecavity between the base of the thin-walled member 115a and the edge ofthe thick-walled member 115b and it is separated from the propellant 131by an easily frangible moisture seal 119. The cartridge casing 113 hasthe same general configuration as the cartridge casing in FIG. 1 withthe exception of an annular crimp dimple 11311 in the larger diameterbore 113b, which results in an annular indentation 1131) being formed onthe exterior of the cartridge casing that limits the forwardlongitudinal movement of the primer. Upon being struck by the head of afiring pin 61 at the end of a forward stroke, the base of thethin-walled member 115a is crushed forwardly and pressed against the endof the thick-walled member 115b which serves as a circumferential anvilto pinch a portion of the primer charge 117a therebetween to ignite theprimer charge which in turn fires the propellant contained in the largerforward bore, and is thereupon moved rearwardly in substantially thesame manner as hereinbefore described in relation to the cartridge shownin FIG. 1.

In FIG. 6 is shown still another embodiment, generally indicated at 211,in which the cup-shaped piston primer 215 is composed of a single piecehaving a cylindrical guide portion 215a which freely slidably engagesthe small diameter bore in the base of the cartridge casing with anannular, outwardly flared, flanged obturator portion 215b, the annularobturator lip 2151) of which slidably engages the large diameter bore ofthe cartridge casing in a light interference fit. The central tubularwall of the cylindrical, piston portion 215a is relatively thick forradial strength, and has a relatively thin-walled base 2150 whichprotrudes rearwardly and bulges radially from the annular shoulder 215a,as indicated at 2150', at the rear end of the thick-walled tubularsection 215a to form an annular rim chamber 215d. Compacted in the rearand central zone of the cup-shaped piston 215 is a primer charge 217which is separated from the propellant charge 231 contained in theinterior of the cartridge casing 213 by only a thin, easily frangiblepreferably combustible, moisture seal 219 of suitable material such aswax or Krylon. Upon being struck by the head of a firing pin at the endof its forward stroke, the thinwalled overlapping base 2150 is crushedand the bulging annular rim section 215d is pressed against the end ofthe thick tubular wall 215a which serves as a circumferential anvil topinch a portion of the primer charge 217a between the bulging oroverlapping rim portions 215d of the thin-walled base 215a, therebyigniting the primer charge 217, which in turn ignites the propellant 231contained in the interior of the cartridge casing to effect forwardmotion of the projectile and rearward energy transfer motion of thepiston primer 215, as hereinbefore described in relation to thecartridge shown in FIG. 1.

That which is claimed is:

1. In a cartridge of the primer set-back type including a casing havingan open forward end with a projectile p engage the forward stopretaining means and with a base portion rearward of the tubular wallportion being relatively thinner and more deformable than the tubularportion and adapted to be deformed and 'pressed against the rearward endof the relatively thick tubular portion upon being struck by the head ofa firing pin to effect percussion firing of the primer mixture containedtherein. 2. In a cartridge of the primer set-back type according toclaim 1, the improvement further comprising:

said cartridge casing having a second bore formed therein of largerdiameter and coaxial with the first bore and connected thereto by anannular beveled shoulder and adapted to contain the propellant there-1n, an annular flared flange portion formed at the open end of thecup-shaped piston primer and disposed in the larger diameter bore in thecartridge casing with the sides of the flanged portion engaging thelarger diameter bore in a light interference fit and adapted to obturateupon ignition of the propellant to form a seal against the rearwardleakage of the resulting propellant gas through the bore in the base ofthe cartridge. 3. In a cartridge of the primer set-back type accordingto claim 2 wherein:

the edge of said annular flared flange portion having a thicknesssubstantially less than the thickness of the tubular wall portion. 4. Ina cartridge of the primer set-back type according to claim 2 wherein:

the back side of the flared flanged portion formed at the open end ofthe cupshaped piston primer being adapted to engage the annular beveled.shoulder connecting the coaxial bores formed in the casing to limit therearward movement of the cup-shaped piston primer upon ignition of thepropellant charge, and the forward end of the flared flange portion ofthe cup-shaped piston primer engaging the forward stop retaining meansto limit the forward motion of the piston primer upon being struck bythe head of a firing pin. 5. In a cartridge of the primer set-back typeaccording to claim 3:

said cup-shaped piston primer having a unitary construction with itsbase portion extending rearwardly from the relatively thicker and lessdeformable tubular wall portion and having a common interior diametertherewith but being adapted to be readily deformed and pressed againstthe end of the relatively thicker tubular wall upon being struck by thehead of a firing pin to form a circumferential anvil to ignite theprimer mixture contained therein. 6. In a cartridge of the primerset-back type according to claim 3 wherein:

said cup-shaped piston primer having a unitary construction with thebase portion outwardly from the rearward interior portion of therelatively thicker and relatively less deformable tubular wall to forman overlap which serves as a circumferential anvil adapted to be readilydeformed and pressed against the end of the relatively thicker tubularwall upon being struck by the head of a firing pin to ignite the primermixture contained therein. 7. In a cartridge of the primer set-back typeaccording to claim 3 wherein:

said cup-shaped piston primer being formed by a tubular wall disposedinside a relatively thinner and more deformable cup-shaped member withthe rearward portion of the relatively thinner and more derearward endof the relatively thicker and relatively formable cup-shaped memberextending beyond the References Cited UNITED STATES PATENTS lessdeformable tubular wall to form a cavity adapted 624 146 5/1899 Young102 38 to be readily deformed and pressed against the rear- 740:79010/1903 Young et aL 102 45 ward end of the relatively thicker tubularwall which 5 2 394,249 2 194 McG-ahey 102 3 serves as a circumferentialanvil upon being struck 2,537,443 1/1951 cerrella 89-156 by the head ofa firing pin to ignite the primer mixture contained therein ROBERT F.STAHL, Primary Examiner

